A combination square is an instrument widely used by carpenters, mechanics, tool makers, artisans, handy men and the like, in woodworking and metalworking. The combination square is composed of a scaled blade and an adjustable body that typically slides in a longitudinal groove formed in the blade. The longitudinal position of the blade relative to the body may be releasably locked.
A number of combination squares are known to use a transverse rib, advanced by a thumbscrew to lock the position of the blade relative to the body. In these squares, the rib abuts against the groove of the blade. This can be cumbersome for the a number of reasons, some of which are set forth in the following text.
Considerable time and effort is required to tighten or loosen the thumbscrew when attempting to lock or release the position of the blade relative to the body.                1. The blade does not slide well once the transverse rib has been released.        2. The blade may easily slip free from the body once the transverse rib has been released.        3. Reinsertion of the transverse rib back into the groove is generally difficult.        
Attempts to overcome the transverse rib problem have resulted in squares having a body that is clamped directly against the face of the blade, bearing a horizontal clamping force on the blade to secure the blade. In these squares, the horizontal clamping force acts on a comparatively random area on the blade, thereby reducing the accuracy of the combination square.
Additionally, a number of combination squares are known to be generally formed with smooth surfaces set at 90° and 45° which can abut a work piece, for constructing or checking 90° and 45° angles, respectively. One difficulty that exists when working with such squares occurs when a guiding surface of a work piece is not at perfect right angles to the working surface of the work piece on which markings or cuts are to be made. Examples include situations where a working surface and/or a work piece have radiused, chamfered, or otherwise irregular surfaces.
Thus, a need exists to overcome the problems with the prior art systems, designs, and processes as discussed above.
It is to be understood that, if any prior art information is referred to herein; such reference does not constitute an admission that the information forms part of the common general knowledge in the art, in Australia or any other country.